Four-channel headphone

ABSTRACT

A four-Channel headphone comprises a pair of left and right headphone body casings, a front channel speaker and a rear channel speaker respectively provided in each casing and electrical signal supplying means for supplying rear channel signals to the rear channel speakers with shifted phase. When the signals shifted in phase are reproduced and sounded from the rear channel speakers in the headphone body casings, the sounds produce a panoramic surrounding sound effect for a listener who uses the four-channel headphone.

United States Patent [1 1 Ohta FOUR-CHANNEL HEADPHONE [75] Inventor:

[73] Assignee: Victor Company of Japan, Ltd.,

Kanagawa-ken, Japan [22] Filed: Dec. 2, 1971 [21] Appl. No.: 204,148

Kazuho Ohta, Sagamihara, Japan [30] Foreign Application Priority DataDec. 5, 1970 Japan 45-107810 [52] US. Cl. 179/156 R, 179/1 GQ [51] Int.Cl H04r 5/02, H04r 5/04, H04m 1/05 [58] Field of Search 179/1 GP, 156R[56] References Cited UNITED STATES PATENTS 3/1964 Pflager et al. 179/1GP 5/1967 Renwick 179/1 GP Mar. 112, 1974 Beidler.... 179/156 R Kennedy179/1 GP Primary Examiner-William C. Cooper Attorney, Agent, orFirm-Holman & Stern [5 7] ABSTRACT A four-Channel headphone comprises apair of left and right headphone body casings, a front channel speakerand a rear channel speaker respectively provided in each casing andelectrical signal supplying means for supplying rear channel signals tothe rear channel speakers with shifted phase. When the signals shiftedin phase are reproduced and sounded from the rear channel speakers inthe headphone body casings, the sounds produce a panoramic surroundingsound effect for a listener who uses the four-channel headphone.

7 Claims, 8 Drawing Figures PAIENIEDHAR 12 1974 3.796, 840

SHEET 2 OF 4 1 FOUR-CHANNEL HEADPHONE The invention relates to afour-channel headphone and, more particularly, to a four-channelheadphone in which four speakers respectively corresponding to each offour channels are mounted for producing a panoramic surroundingfour-channel sound effect which gives a listener an impression that heis entirely surrounded by sound.

In a system for reproducing an audio signal, there has recently beenemployed a reproducing apparatus including a four-channel tape or afour-channel record for reproducing a sound field which closelyresembles to the original sound field. There have been proposed variousarrangements of speakers in a reproducing apparatus for four-channelsystem. The most prevailing speaker arrangement is a so-called 22 systemin which speakers for first, second, third and fourth channels arerespectively disposed at left front, left rear, right front and rightrear of the listener. In this system, four-channel signals have a soundimage orientation corresponding to a sound source and different phases,levels and information contents in connection with reproducibility of asound field. A listener placed in the center of this speakerarrangementhas an impression that he exists at the center of the sound fieldsurrounded by sound all around, due to a sound field effect produced bysound planes formed between respective speakers which reproduce andsound the fourchannel signals.

With a view to affording this four-channel effect to a headphone, afour-channel headphone has been proposed. This headphone has fourspeakers in its two headphone bodies, namelytwo in the left headphonebody and two in the right one and the respective speakers are adapted toreproduce four-channel signals. However, the four-channel headphonesystem is different from the system in which the speakers are arrangedin a large space in a room to form a sound field in a room space,because in the headphone system both ears of the listener arerespectively in tight contact with the left and right headphone bodiesand each ear receives only sound produced in the space of either left orright headphone body. Consequently, in the fourchannel headphone inwhich the left front and left rear speakers corresponding to the firstand second channels are mounted on the left headphone body andthe rightfront and right rear speakers corresponding to the third and fourthchannels on the right headphone body, the sounds of the first and secondchannels are mixed together in the left headphone body and reaches onlythe left ear of the listener whereas the sounds of the third and fourthchannels are mixed in the right headphone and reaches only theright earof the listener. In this case, the sounds of the left side channel (thefirst and second channels) and those of the right side channel (thethird and fourth channels) are not mixed in the air and neither thesounds of the left side channels nor those of the right side channelsreach the listeners ear on the opposite side. Further, the headphoneessentially has a limitation in its size and the two speakers mounted ineither headphone body are relatively close to each other. This preventsthe listener from having impresssion of spread of sound between the twospeakers.

As a result, the prior art four-channel headphone is disadvantageous inthat the left and right headphone bodies which have two speakersrespectively reproduce sounds of four different channels but theheadphone can only give the listener a binaural effect produced by thesound from the left headphone body and the sound from the rightheadphone body, and cannot give the listener a panoramic surroundingsound effect which gives the listener an impression that he is reallyand entirely surrounded by the sound. Further, the conventionalheadphone is disadvantageous in that the listener has a feeling that thesounds concentrate on his occipital region which is quite unpleasant tohim.

The inventor of the present invention has discovered that if the signalswhich should be reproduced and sounded from the rear channel speakers,i.e., the second and the fourth channel speakers, of the above describedfour-channel headphone have been shifted in phase from the second andfourth channel signals which were originally to be reproduced, thelistener using the headphone can obtain a truly effective panoramicsurrounding sound effect. The reason for the above effect istheoretically quite unclear. It is presumed, however, that the effect isdue to the construction of the headphone itself according to which thesounds of the first and second channels and those of the third andfourth channels respectively reach the left ear and the right earseparately, since in case in the room disposed with four-channelspeakers the signals of the second and fourth channels are reproducedand sounded with their phases shifted from the signals of the second andfourth channels which were originally to be reproduced, it only givesthe listener an unpleasant feeling, whereas the above described effectis produced in the headphone.

It is, therefore, a general object of the invention to provide a noveland useful four-channel headphone which has eliminated the abovedescribed disadvantages of the conventional headphone.

Another object of the invention is to provide a fourchannel headphonewhich produces a panoramic surrounding sound field effect and gives alistener an impression of spread or expanse of sound.

A further object of the invention is to provide a fourchannel headphonein which each pair of the speakers provided in each of the left andright headphone bodies reproduce and sound signals which have a phasedifference between-each-other. According to the headphone of theinvention, the listener has an impression that he is surrounded bysounds and has a feeling of reality which is much superior to thebinaural effect produced by the prior art headphone. Further, thelistener feels a spread of sound. Furthermore, he has no unpleasantfeeling that the sound concentrates on his occipital region. t

Other objects and features of the invention will become apparent fromthe description made hereinbelow with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic plan view of the speaker arrangement of thefour-channel headphone according to the invention shown in its state inuse;

FIG. 2 is an elevational view showing one embodiment of the four-channelheadphone according to the invention;

FIG. 3 is a side view of the four-channel headphone shown in FIG. 2taken along the line III-Ill;

FIG. 4 is a left side view of the four-channel headphone shown in FIG.2;

FIG. 5 is a sectional plan view of the headphone taken along the line VVof FIG. 4;

FIG. 6 is a circuit diagram of one embodiment of the electric circuit ofthe four-channel headphone according to the invention;

FIG. 7 is a circuit diagram of another embodiment of the electriccircuit of the four-channel headphone according to the invention; and

FIG. 8 is a diagram showing a frequency-phase shift characteristic.

FIG. 1 shows a schematic plan view of the fourchannel headphoneaccording to the invention shown in its state in use. A four-channelheadphone 10 generally comprises a left headphone body 11 and a rightheadphone body 12. In a casing 3 of the left headphone body 11, thereare a first channel speaker 14 and a second channel speaker 15 mountedat positions at which a line connecting the centers of the two speakersruns substantially parallel to a line connecting through the front andback of the listener's head. Similarly, a third channel speaker 18 and afourth channel speaker 19 are arranged in a casing 17 ofthe rightheadphone body 12 at positions at which a line connecting the centers ofthe two speakers runs substantially parallel to a line connecting thefront and back of the listeners head. Signals which are applied to thesefirst to fourth channel speakers 14, 15, 18, 19 are the same first tofourth channel signals as are applied to the conventional 22 systemspeakers disposed at left front, left rear, right front and right rearpositions to the listener. The casings 13 and 17 are respectivelyprovided in the middle of their outside surface with phase shiftingslide switch knobs 20 and 21 to be described later.

One embodiment of a concrete construction of the four-channel headphoneaccording to the invention with the above described speaker arrangementis illustrated in FIGS. 2 to 5. Throughout these figures, illustrationis made only for the left headphone body 11. As to the right headphonebody 12, description of a concrete construction thereof is omittedbecause the right headphone body 12 has exactly the same construction asthe left headphone body 11 except only that the first and second channelspeakers 14 and 15 are replaced by thethird and fourth speakers 18 and19.

The left and right headphone bodies 11 and 12 are connected with eachother by means of a curved and elastic support plate 32 which is securedat either end thereof to holding frames and 31 which, in turn, arerespectively pivotally supported on the casings 13 and 14. The supportplate 32 is covered with a head pad 33 made of a soft material. Anelectrical signal transmitting code 34 to be connected to a headphonejack of the reproducing apparatus is connected in the lower portion ofthe casing 13 ofthe left headphone body 11. A code 35 for transmittingthe third and fourth channel signals extends from the upper portion ofthe casing 13 through the head pad 33 and is connected to the upperportion of the casing 14 of the right headphone body 12. The casing 13and 14 are both provided with car pads 36 and 37 made of a soft materialat the surfaces which contact the listener's ears and portions of thehead around the ears.

The ear pad 36 is of an annular shape with openings 38 which are largeenough to receive the listeners ears. The speakers 14 and 15respectively generally consist of magnetic poles 39 and 40, magnets 41and 42 and diaphragms 43 and 44 which are respectively mounted on a unitmounting plate 45 with an angle of less than 180 relative to each otheras shown in cross section in FIG. 5. In the present embodiment, theangle made between planes which are vertical to the central axes of themagnets 41 and 42 of the speakers 14 and I5'is and the angle madebetween the directions of the center of radiation of sound which areequal to the ccntral axes of the magnets 41 and 42 is 30. The speakers14 and 15 are disposed at positions at which the line connecting thecenters ofthe two speakers runs parallel to the line connecting thefront and back of the listeners head as shown in the side view of FIGS.3 and 4. The front surfaces of the diaphragms 43 and 44 are covered withan acoustic planes 46 made of a punching metal. The speakers 14 and 15are separated from each other by partitions 47, 47 so that the soundswill not leak into the other speaker side on the rear side of thespeakers 14 and 15 (on the side of the magnetic poles and the magnets).Between the two partitions 47, 47, there is provided a phase shiftingslide switch 48 with its knob 20 exposed outside of the casing 13.

Nextly, the circuit diagram of the first embodiment of the electriccircuit of each speaker including the phase shifting switch is shwn inFIG. 6. Terminals 60, 61, 62 and 63 for the first to fourth speakers 14,15, 18 and 19 are respectively connected to amplifiers of the first tofourth channels in the reproducing apparatus through the code 34. As tothe front channels, i.e., the first and third channels, the speakers 14and 18 are directly connected to the terminals 60 and 62. The speakers15 and 19 of the rear channels, i.e., the second and fourth channels areconnected to the terminals 61 and 63 through phase shifting switches 48and 49 respectively provided in the casings 13 and 17.

When the switches 48 and 49 are connected on the side of contacts a bymeans of the knobs 20 and 21, the speakers 15 and 19 are connected tothe terminals 61 and 63 in the same phase with the original phase.Accordingly, the second and fourth channel signals are reproduced andsounded from the speakers 15 and 19 in their original phase. When, onthe other hand, the knobs 20 and 21 are slid to connect the switches 48and 49 on the side of contacts h, the speakers 15 and 19 are connectedto the terminals 61 and 63 in opposite phase. Accordingly, the secondand fourth channel signals are reproduced and sounded in a phaseopposite to the original phase.

If, accordingly, the switch knobs 20 and 21 provided on the casings 13and 17 of the headphone bodies 11 and 12 are operated to connect theswitches 48 and 49 on the side of the contacts I), the second and fourthchannel signals are respectively reproduced and sounded from the secondand fourth channel speakers 15 and 19 of the headphone bodies 11 and 12in opposite phase to the original phase of the second and fourth channelsignals, i.e., with a phase difference of The second and fourth channelsignals have phases (normally, phases having slight phase differencesiAO) which are related with the first and third channel signals, so thatthe reproduced sounds of the second and fourth channels have a largephase difference (180 :tAO) relative to the reproduced sounds of thefirst and third channels. Accordingly, if the listener applies theheadphone body 11 containing the speakers 14 and 15 to the left ear andthe headphone body 12 containing the speakers 18 and 19 to the rightear, the panoramic surrounding sound effect which gives him animpression that he is surrounded by the sound is'produced. In this case,he is entirely free from the feeling that the sounds concentrate on hisoccipital region. Further, the sound of each channel in the four-channelsystem is different from one another and the signals of the rearchannels (the second and fourth channels) seldom coincide in phase andlevel with the signals of the front channels (the first and thirdchannels). Accordingly, the sounds of the front channels are notgreately cancelled by the sounds of the rear channels.

In the foregoing embodiment, the changing of phase between an originalphase and an opposite phase is effected by means of the phase shiftingswitches 48 and 49. Instead of provision of the switches 48 and 49, thespeakers and 19 may be fixedly connected to the terminals 61 and 63 inopposite polarity, so that the signals may be reproduced in oppositephase to the original phase.

F IG. 7 shows a circuit diagram of the second embodiment of the electriccircuit of the four-channel speakers according to the invention. In theabove described embodiment in which the phases of the second and fourthchannel signals reproduced and sounded are changed by 180 to make themopposite phase to the original phases, the above described surroundingeffect is produced. This construction, however, has a problem that thelistener may sometimes have an unpleasant feeling due to unnaturalnessaccompanying such surrounding effect. Furthermore, if the first and thesecond (or the third and the fourth) channel signals hap-v pen tocompletely in the same phase and same level, the sound of the firstchannel signal will be cancelled by the sound of the second channelsignal which is in opposite phase to the sound of the first channel.This particularly apts to become a problem in low frequencies in whichthe two signals often have components which are in phase or almost inphase with each other. The present invention is directed to settle theseproblems by variably adjusting the phase shift so that a naturalsurrounding sound effect will be produced in accordance with phases ofthe signals.

In FIG. 7, the speakers 14 and 18 for the front channels, i.e., thefirst and the third channels, are directly connected to the terminals 60and 62, as in the first embodiment previously described. The speakers 15and 19 for the rear channels, i.e., the second and the fourth channels,are respectively connected to the terminals 61 and 63 through phaseadjusting circuits 70 and 71. The phase adjusting circuits 70 and 71generally consist of transformers 72 and 73, variable resistors 74 and75 and capacitors 76 and 77. One end of a voice coil of the speaker 15is connected to a connecting point of the variable resistor 74 and thecapacitor 76. One end of a voice coil of the speaker 19 is likewiseconnected to a connecting point of the variable resistor 75 and thecapacitor 77. The other ends of the voice coils of the speakers 15 and19 are respectively connected to one ends of primary windings andintermediate taps 78 and 79 of the secondary windings of thetransformers 72 and 73.

In the present embodiment, slide knobs of the variable resistors 74 and75 are provided on the casings 13 and 17 of the headphone bodies 11 and12 instead of the switch knobs 20 and 21 employed in the firstembodiment. As shown in FIG. 8, the phase shift of the signals appliedfrom the terminals 61 and 63 to the speakers 15 and 19 through the phaseadjusting circuits and 71 and reproduced and sounded from these speakers15 and 19 varies with frequency. The phase shift is small in lowfrequencies whereas it is large in high frequencies, amounting nearly to180. A frequency f at which the phase shift is 90 is represented byequation f 1/21rCR, where C is capacitance value of the capacitors 76and 77 and R is resistance value of the variable resistors 74 and 75.

Accordingly, the value of the frequency f is changed by changing thevalue of resistance of the variable resistors 74 and 75 and thecharacteristic shown by a full line in FIG. 8 varies as shown by abroken line and a chain line in the same figure. If the frequency f isselected at about 200 Hz to 1,000 I-Iz, an excellent effect is producedwith respect to a sound image orientation and a sound fieldreproducibility.

According to the circuit of the present embodiment, a natural panoramicsurrounding sound effect can be obtained. Moreover, the cancellation ofthe level in low frequencies can be avoided.

In the present embodiment, the amount of phase shift varies inaccordance with frequency. However, the invention is not limited to thisbut a constant amount of phase shift may be maintained over the wholerange of frequency or the amount of phase shift may be made variableover the whole range of frequency.

Further, this invention is not limited to these embodiments but variousvariations and modifications may be made without departing from thescope and spirit of the invention.

What I claim is: j

1. A four-channel headphone comprising:

a. a pair of left and right headphone body casings respectively appliedto the left and right ears of a listener;

b. first andsecond speakers disposed in said left headphone body casingso that when said headphone is applied to the ears of the listener saidfirst speaker is to the front of the left ear of the listener and saidsecond speaker is to the rear of the left ear of the listener;

0. third and fourth speakers disposed in said right headphone bodycasing so that when said headphone is applied to the ears of thelistener said third speaker is to the front of the right ear of thelistener and said fourth speaker is to the rear of the right ear of thelistener;

. first means for supplying to said first speaker a first channel signalwhich corresponds to a sound emanating from the front and left of thelistener;

. first switch means mounted in said left head-phone body casing andbeing set to selectively reverse connections, said first switch meanshaving input terminals and output terminals, said output terminals beingelectrically connected to said second speaker;

f. second means for supplying across said input terminals of said firstswitch means a second channel signal which corresponds to a soundemanating from the rear and leftof the listener;

g. third means for supplying to said third speaker a third channelsignal which corresponds to a sound emanating from the front and rightof the listener;

h. second switch means mounted in said right headphone body casing andbeing set'to selectively reverse connections, said second switch meanshaving input terminals and output terminals, said output terminals ofsaid second switch means being electrically connected to said fourthspeaker; and

i. fourth means for supplying across said input terminals of said secondswitch means a fourth channel signal which corresponds to a soundemanating from the rear and right of the listener.

2. The four-channel headphone as defined in claim 1, wherein said firstswitch means comprises a double pole double throw switch, the switchknob of which is exposed outside of said left headphone body casing, andwherein said second switch means comprises a double pole double throwswitch, the switch knob of which is exposed outside of said rightheadphone body casing.

3. The four-channel headphone as defined in claim 2 which furthercomprises two spaced partitions provided in said left headphone bodycasing for separating in space said first speaker from said secondspeaker,

said first switch means being provided between said two spacedpartitions, and two spaced partitions provided in said right headphonebody casing for separating in space said third speaker from said fourthspeaker, said second switch means being provided between said two spacedpartitions.

4. A four-channel headphone comprising:

a. a pair of left and right headphone body casings respectively appliedto the left and right ears of a listener;

b. first and second speakers disposed in said left headphone body casingso that when said headphone is applied to the ears of the listener saidfirst speaker is to the front of the left ear of the listener and saidsecond speaker is to the rear of the left ear of the listener;

c. third and fourth speakers disposed in the right headphone body casingso that when said headphone is applied to the ears of the listener saidthird speaker is to the front of the right ear of the listener and saidfourth speaker is to the rear of the right ear of the listener;

d. first means for supplying to said first speaker a first channelsignal which corresponds to a sound emanating from the front and left ofthe listener;

e. first phase-shifting means mounted in said left headphone body casingfor shifting in phase a signal which is applied to said firstphase-shifting means;

f. second means for supplying through said first phase-shifting means tosaid second speaker a second channel signal which corresponds to a soundemanating from the rear and left of the listener;

g. third means for supplying to said third speaker a third channelsignal which corresponds to a sound emanating from the front and rightof the listener;

h. second phase-shifting means mounted in said right headphone bodycasing for shifting in phase a signal which is applied to said secondphase-shifting means;

i. fourth means for supplying through said second phase-shifting meansto said fourth speaker a fourth channel signal which corresponds to asound emanating from the rear and right of the listener.

5. The four-channel headphone as defined in claim 4, wherein each of thefirst and second phase-shifting means comprises a transformer, a seriescombination of a variable resistor and a capacitor, which seriescombination is connected across the secondary winding of saidtransformer, said secondary winding having an intermediate tap, saidsecond speaker and said fourth speaker being respectively connectedbetween said intermediate tap and the connecting point of said variableresistor and said capacitor, and wherein the second and fourth meanssupply respectively said second channel signal and said fourth channelsignal to the primary winding of said transformer.

6. The four-channel headphone as defined in claim 5 wherein theresistance adjusting knobs of the variable resistors in the first andsecond phase-shifting means are exposed respectively outside of the leftand right headphone body casings.

7. The four-channel headphone as defined in claim 6 which furthercomprises two spaced partitions provided in said left headphone bodycasing for separating in space said first speaker from said secondspeaker, said first phase-shifting means being provided between said twospaced partitions, and two spaced partitions provided in said rightheadphone body casing for separating in space said third speaker fromsaid fourth speaker, said second phaseshifting means being providedbetween said two spaced partitions.

1. A four-channel headphone comprising: a. a pair of left and rightheadphone body casings respectively applied to the left and right earsof a listener; b. first and second speakers disposed in said leftheadphone body casing so that when said headphone is applied to the earsof the listener said first speaker is to the front of the left ear ofthe listener and said second speaker is to the rear of the left ear ofthe listener; c. third and fourth speakers disposed in said rightheadphone body casing so that when said headphone is applied to the earsof the listener said third speaker is to the front of the right ear ofthe listener and said fourth speaker is to the rear of the right ear ofthe listener; d. first means for supplying to said first speaker a firstchannel signal which corresponds to a sound emanating from the front andleft of the listener; e. first switch means mounted in said lefthead-phone body casing and being set to selectively reverse connections,said first switch means having input terminals and output terminals,said output terminals being electrically connected to said secondspeaker; f. second means for supplying across said input terminals ofsaid first switch means a second channel signal which corresponds to asound emanating from the rear and left of the listener; g. third meansfor supplying to said third speaker a third channel signal whichcorresponds to a sound emanating from the front and right of thelistener; h. second switch means mounted in said right headphone bodycasing and being set to selectively reverse connections, said secondswitch means having input terminals and output terminals, said outputterminals of said second switch means being electrically connected tosaid fourth speaker; and i. fourth means for supplying across said inputterminals of said second switch means a fourth channel signal whichcorresponds to a sound emanating from the rear and right of thelistener.
 2. The four-channel headphone as defined in claim 1, whereinsaid first switch means comprises a double pole double throw switch, theswitch knob of which is exposed outside of said left headphone bodycasing, and wherein said second switch means comprises a double poledouble throw switch, the switch knob of which is exposed outside of saidright headphone body casing.
 3. The four-channel headphone as defined inclaim 2 which further comprises two spaced partitions provided in saidleft headphone body casing for separating in space said first speakerfrom said second speaker, said first switch means being provided betweensaid two spaced partitions, and two spaced partitions provided in saidright headphone body casing for separating in space said third speakerfrom said fourth speaker, said second switch means being providedbetween said two spaced partitions.
 4. A four-channel headphonecomprising: a. a pair of left and right headphone body casingsrespectively applied to the left and right ears of a listener; b. firstand second speakers disposed in said left headphone body casing so thatwhen said headphone is applied to the ears of the listener said firstspeaker is to the front of the left ear of the listener and said secondspeaker is to the rear of the left ear of the listener; c. third andfourth speakers disposed in the right headphone body casing so that whensaid headphone is applied to the ears of the listener said third speakeris to the front of the right ear of the listener and said fourth speakeris to the rear of the right ear of the listener; d. first means forsupplying to said first speaker a first channel signal which correspondsto a sound emanating from the front and left of the listener; e. firstphase-shifting means mounted in said left headphone body casing forshifting in phase a signal which is applied to said first phase-shiftingmeans; f. second means for supplying througH said first phase-shiftingmeans to said second speaker a second channel signal which correspondsto a sound emanating from the rear and left of the listener; g. thirdmeans for supplying to said third speaker a third channel signal whichcorresponds to a sound emanating from the front and right of thelistener; h. second phase-shifting means mounted in said right headphonebody casing for shifting in phase a signal which is applied to saidsecond phase-shifting means; i. fourth means for supplying through saidsecond phase-shifting means to said fourth speaker a fourth channelsignal which corresponds to a sound emanating from the rear and right ofthe listener.
 5. The four-channel headphone as defined in claim 4,wherein each of the first and second phase-shifting means comprises atransformer, a series combination of a variable resistor and acapacitor, which series combination is connected across the secondarywinding of said transformer, said secondary winding having anintermediate tap, said second speaker and said fourth speaker beingrespectively connected between said intermediate tap and the connectingpoint of said variable resistor and said capacitor, and wherein thesecond and fourth means supply respectively said second channel signaland said fourth channel signal to the primary winding of saidtransformer.
 6. The four-channel headphone as defined in claim 5 whereinthe resistance adjusting knobs of the variable resistors in the firstand second phase-shifting means are exposed respectively outside of theleft and right headphone body casings.
 7. The four-channel headphone asdefined in claim 6 which further comprises two spaced partitionsprovided in said left headphone body casing for separating in space saidfirst speaker from said second speaker, said first phase-shifting meansbeing provided between said two spaced partitions, and two spacedpartitions provided in said right headphone body casing for separatingin space said third speaker from said fourth speaker, said secondphaseshifting means being provided between said two spaced partitions.